Feinmann here discusses the political activist and Romantic author José Esteban Antonio Echeverría (1805–1851) in particular for his criticism of the tyrannical rule of Juan Manuel de Rosas (1793–1877). Rosas was head of the Federalist Party. And while the Federalist position is arguably the more important carrier of the democratic tradition in 19th-century Argentine than their centralist Unitarian opponents, Rosas' rule of the Province of Buenos Aires beginning in 1929 and later extended to the Argentine Confederation was one of the ugliest episodes of brutality and state-terrorist rule in Argentine history.
Echeverría was a partisan of the Unitarians and, as Feinmann describes him, an especially bitter critic of the despicable Rosas.
(Update 05/31/2015: In re-reading this, I realize that the version of Rosas that I sketched here is far too oversimplified. Feinmann here in this is describing the work of Esteban Echeverria, a contemporary who took a decidedly unfriendly view toward Rosas, but whose view on Rosas isn't the last word in historical judgment.
The long-standing mainstream view of Rosas as a villain is part of the conservative historical view identified with Bartholomé Mitre [1821–1906]. A non-Mitrist view of Rosas that enjoys support among Peronistas views him in a more nuanced light. Among them Argentine President Cristina Fernández.)